Tensile Strength Calculation for Gas Arc Welding

Start by learning the symbols and name of the welds. The strength calculations are different for the various welds;

Weld Symbols

An idea of strength calculations

I just web searched these!

What is the pipe material grade of steel ? Normal selection is based by matching the strength of the material and the filler material or electrode. How did you select the electrode and at what parameters did you weld them?

the electrode designator normally gives you the tensile strenght of the weldment example

E60XXX : Tensile Strength = 60Ksi or 414 MPa; Yield Strength = 48Ksi or 313 MPa

E70XXX : Tensile Strength = 70Ksi or 482MPa; Yield Strength = 58Ksi or 399 MPa

So lots more than you can simple calculate the strenght, Ref to AWS code for complete details and know-how.

Since the OP specifies Gas Arc Welding, I would assume that he refers to GTAW and in that case, the electrode is not consumable.

The best source of Engineering dta, that I have found is AWS 1.1. This reference can be obtained from the American Welding Society and should be a part of every welder's library. It has all of the welding characteristics and Formulae to assist you. It also contains welding discontinuities that will have a deliterious effect on the weld and parent materiel.

Get a copy of Design of Weldments, by Omar Blodgett, from Lincoln Arc Welding Institute in Euclid Ohio. It's cheap and one of the best design books around for any simple part, whether welded, machined, cast, etc.